1. Field of the Invention
The invention relates to a method of manufacturing an optoelectronic device comprising a mesa, preferably a semiconductor diode laser often referred to as laser hereinafter for short, whereby a semiconductor body is formed through the provision on a substrate of at least in that order: a first cladding layer, preferably of a first conductivity type, an active layer, a second cladding layer preferably of a second conductivity type opposed to the first, and preferably a contact layer of the second conductivity type, and whereby a preferably strip-shaped mesa is formed at the surface of the semiconductor body so as to comprise at least a major portion of the second cladding layer, through the provision of a mask on the surface of the semiconductor body, and through the subsequent removal from the semiconductor body of semiconductor material situated outside the mask through etching down to or down to close to an etching stopper layer which forms part of the semiconductor body.
Such a method is particularly suitable for the manufacture of lasers of the--possibly buried--heterojunction or ridge waveguide type. LEDs (=Light Emitting Diodes) or waveguides may also be manufactured in this manner. In the present Application, accordingly, the term "active layer" is understood also to cover a radiation guiding layer. A laser of the (buried) ridge waveguide type which emits at or below 1 .mu.m is particularly suitable for use in an optical disc system such as a system for optical registration, and for use as a pumping laser in a glass fiber communication system.
2. Description of the Related Art
Such a method of manufacturing a laser of the buried ridge waveguide type is known from a European Patent document published Mar. 25, 1992 under no. 0.477.013. The semiconductor body of the laser (see FIG. 1) is manufactured (see FIG. 2) in that the following are provided in that order on a GaAs substrate: a first cladding layer of AlGaInP, an active layer of GaInP, a second cladding layer of AlGaInP, and a GaAs contact layer. The second cladding layer is subdivided into a thin and a thick portion between which an etching stopper layer is provided. A strip-shaped mesa is formed in that a mask is provided and subsequently the semiconductor material outside the mask is removed down to the etching stopper layer by means of preferential etching with an etchant based on H.sub.2 SO.sub.4. The mesa is given a trapezium-shaped cross-section in that manner.
A disadvantage of the known method is that the laser manufactured thereby shows a kink in the relation between the emitted optical power and the current through the laser at comparatively low powers. Owing to this kink, the characteristic is not linear, which restricts the usefulness of the laser, for example in a system for optical registration.